They can be a real pain to get into ... and even when you get in they can be just as much of a pain if you want to get into another category ... and the funny part is it really has nothing to do with images or drop shipping ... I think it has much more to do with SEO and where google puts you.

I say this because 5 years ago I was really doing well with SEO and Amazon asked me to join (Sexual wellness) ... A year later after having lingerie removed for being in the wrong category I asked to join the lingerie category and jumped through all kinds of hoops and they still said no ...

But if it helps you feel better, Amazon is such a price war, that being a simple drop shipper (price you pay for items) you will always be chasing your tail just to make a $1 and you will never really make money there unless you get distributor pricing (at least 30% below wholesale) on items. Or if you can get a company to give you exclusive sales to an item so you are not in a price war.